Bismuth manganese titanate: Crystal structure and properties I.V. Piir a, ⁎, N.A. Sekushin a , V.E. Grass a , Y.I. Ryabkov a , N.V. Chezhina b , S.V. Nekipelov c , V.N. Sivkov d , D.V. Vyalikh e a Institute of Chemistry Komi Science Centre UB RAS, 167982 Syktyvkar, Russia b St-Peterburg State University, St-Peterburg, Russia c Komi Pedagogical Institute, 167982 Syktyvkar, Russia d Department of Mathematics Komi Science Centre UB RAS, 167982 Syktyvkar, Russia e Technical University of Dresden, D-01062, Dresden, Germany abstract article info Article history: Received 9 September 2011 Received in revised form 7 December 2011 Accepted 28 February 2012 Available online 23 March 2012 Keywords: Pyrochlore Bismuth manganese titanate Bi–Mn–Ti–O NEXAFS Magnetic behavior Electrical properties Manganese-containing bismuth titanate solid solutions with a pyrochlore-type crystal structure were obtained by the ceramic technique over a wide range of compositions. The NEXAFS (near-edge X-ray absorp- tion fine structure) spectra of Mn2p-absorption in bismuth manganese titanate pyrochlores point to manga- nese being mainly in the oxidation state + 2 in these solid solutions. The Mn-rich bismuth titanate pyrochlores showed a superposition of antiferro- (long-order) and ferromagnetic (short-order) behavior. The results of impedance investigations show the electron–ionic conductivity in these samples. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Bismuth-based manganese niobate pyroclores [1] and, apparently, similar titanates related to multifunctional materials [2–8] have attracted considerable attention owing to their scientific interest as well as exciting possibilities for practical applications [1]. In Bi 2 O 3 – Nb 2 O 5 –M 2 O 3 (MO) systems, which have been actively studied in recent years, there are fairly extensive fields of pyrochlores, although in the bi- nary system, bismuth niobate as a pyrochlore is not formed (only the low- and high- temperature BiNbO 4 are known). Many studies of bismuth-based pyrochlores [1–4] have shown that metal atoms in these pyrochlores can occupy both cationic positions—bismuth and niobium—thereby stabilizing the structure of the pyrochlore. Obvi- ously, we can also expect a similar effect for pyrochlore-type bismuth ti- tanate. The pyrochlore Bi 2 Ti 2 O 7 is thermodynamically unstable at high temperature [9–11], is rather sensitive to synthesis conditions and has a tendency to bismuth deficiency. Sleight and coworkers [9] produced a bismuth-deficient composition Bi 1.83 Ti 2 O 6.75 using precursors copreci- pitated from titanium butoxide and bismuth nitrate. Hector and Wiggin [10] prepared Bi 2 Ti 2 O 7 pyrochlore using the coprecipitation route from H 2 O 2 /NH 3 (aq) solutions of titanium with aqueous bismuth nitrate. The stoichiometric material crystallizes into a cubic pyrochlore phase at 470 °C, but the sample calcinated at 500 °C contained Bi 4 Ti 3 O 12 . Recent- ly, Nino and coworkers [11] obtained the dense phase of pure Bi 2 Ti 2 O 7 by coprecipitation synthesis methods followed by microwave sintering techniques and studied the crystal structure, thermal stability, sintering and electrical properties of Bi 2 Ti 2 O 7 ; modified the phase diagram of the Bi 2 O 3 –TiO 2 ; and indicated the thermodynamically unstable pyrochlore phase above 670 °C [11]. Introduction of certain quantities of some metals that are capable of occupying A and B sites of A 2 B 2 O 7 pyrochlore results in an increase in the thermal stability of metal-doped bismuth ti- tanates [13,14] and a wide set of useful properties, depending on the na- ture and quantity of the doping metal. 2. Experimental Manganese-doped bismuth titanate solid solutions with a pyrochlore- type structure were studied. Two series of samples with compositions Bi 2 O 3 :Mn 2 O 3 :TiO 2 as 1:x:2 (I) and 1:x:2.5 (II), where x is varied from 0.01 to 1, were prepared by solid state reactions by mixing Bi 2 O 3 (99.99%), TiO 2 (99.99%) and Mn 2 O 3 (99.98%). The ground powder was sintered at 650 °C for 6 hours and then pressed into disks 10 mm in diam- eter after additional thorough grinding and sintered at 850 °C (10 h), 1000 °C (20 h) and 1100 °C (16 h). All the single-phase samples were tested on metal content. The pycnometric density was measured for a number of samples and compared with the calculated density. The prepared samples of the solid solutions were examined by X-ray diffraction for phase identifications and lattice parameter refinement Solid State Ionics 225 (2012) 464–470 ⁎ Corresponding author. Tel.: + 7 8212219921; fax: + 7 8212218477. E-mail address: piyr-iv@chemi.komisc.ru (I.V. Piir). 0167-2738/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2012.02.051 Contents lists available at SciVerse ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi